The Phase I objective is to develop an improved, prompt-response electronic detector for high energy x-ray portal imaging. The new images will show excellent spatial resolution and signal-to-noise ratio, advantages that will permit ready comparisons of patient alignment images with the treatment plan. These improvements will lead to more reliable and accurate radiation localization, thereby contributing to lower recurrence of tumors at the treatment field margins. Improved spatial resolution portal images will be particularly valuable for treatment of tumors involving the head, neck and prostate, and with the use of gold seeds to assist in the accurate location of a tumor. Experimental work emphasizes amorphous silicon flat panels evaluated with metal-backed phosphor screens and high resolution, high density, fiber optic glass scintillators. The Phase I work will demonstrate the relative merits of these detectors. An advantage for the flat panel detector is the excellent use of available light photons, thus improving detection efficiency as compared to typical lens-coupled camera systems. This project team, led by a company with extensive experience in x-ray imaging, includes a major supplier of therapy machines and imaging systems and a well-known consultant from a leading medical therapy facility, a combination that promises success. PROPOSED COMMERCIAL APPLICATIONS: Electronic imaging fills a need in radiation therapy-by making possible a prompt response technique for monitoring therapy as it takes place. The superior image performance of this new detector will provide improved capability for radiation localization and conformance with the treatment plan. These attractive features enhance commercialization opportunities and help account for the participation of a major equipment supplier as part of this project team.